Liquid crystal display

ABSTRACT

A liquid crystal display is provided, which includes: a first panel including a first signal line, a second signal line intersecting the first signal line, a thin film transistor connected to the first and the second signal lines, and a pixel electrode connected to the thin film transistor and including a first subpixel electrode having a first voltage and a second subpixel electrode capacitively coupled to the first subpixel electrode and having a second voltage; a second panel including a common electrode facing the pixel electrode and supplied with a common voltage; and a vertically aligned liquid crystal layer that is interposed between the pixel electrode and the common electrode, wherein a steepness of light transmittance as function of a voltage applied the first subpixel electrode with respect to the common voltage is lower than about 20.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display.

2. Description of Related Art

A liquid crystal display (LCD) is one of the most widely used flat paneldisplays. An LCD includes two panels provided with field-generatingelectrodes such as pixel electrodes and a common electrode and a liquidcrystal (LC) layer interposed therebetween. The LCD displays images byapplying voltages to the field-generating electrodes to generate anelectric field in the LC layer, which determines orientations of LCmolecules in the LC layer to adjust polarization of incident light.

Among the LCDs, a vertical alignment (VA) mode LCD, which aligns LCmolecules such that the long axes of the LC molecules are perpendicularto the panels in absence of electric field, is spotlighted because ofits high contrast ratio and wide reference viewing angle that is definedas a viewing angle making the contrast ratio equal to 1:10 or as a limitangle for the inversion in luminance between the grays.

The wide viewing angle of the VA mode LCD can be realized by cutouts inthe field-generating electrodes and protrusions on the field-generatingelectrodes. Since the cutouts and the protrusions can determine the tiltdirections of the LC molecules, the tilt directions can be distributedinto several directions by using the cutouts and the protrusions suchthat the reference viewing angle is widened.

However, the VA mode LCD has relatively poor lateral visibility comparedwith front visibility. For example, a patterned VA (PVA) mode LCD havingthe cutouts shows an image that becomes bright as it goes far from thefront, and in the worse case, the luminance difference between highgrays vanishes such that the images cannot be perceived.

In addition, the cutouts and the protrusions reduce the aperture ratio.In order to increase the aperture ratio, the size of the pixelelectrodes is suggested to be maximized. However, the close distancebetween the pixel electrodes causes strong lateral electric fieldsbetween the pixel electrodes, which dishevels orientations of the LCmolecules to yield textures and light leakage, thereby deterioratingdisplay characteristic.

SUMMARY OF THE INVENTION

A liquid crystal display is provided, which includes: a first panelincluding a first signal line, a second signal line intersecting thefirst signal line, a thin film transistor connected to the first and thesecond signal lines, and a pixel electrode connected to the thin filmtransistor and including a first subpixel electrode having a firstvoltage and a second subpixel electrode capacitively coupled to thefirst subpixel electrode and having a second voltage; a second panelincluding a common electrode facing the pixel electrode and suppliedwith a common voltage; and a vertically aligned liquid crystal layerthat is interposed between the pixel electrode and the common electrode,wherein a steepness of light transmittance as function of a voltageapplied the first subpixel electrode with respect to the common voltageis lower than about 20.

An absolute magnitude of a first subpixel voltage defined as the firstvoltage relative to the common voltage may be higher than an absolutemagnitude of a second subpixel voltage defined as the second voltagerelative to the common voltage.

The liquid crystal display may further include a third subpixelelectrode capacitively coupled to the first and the second subpixelelectrodes and having a third voltage.

An area of the first subpixel electrode may be equal to or smaller thanhalf of an area of the second and the third subpixel electrodes.

An absolute magnitude of each of the second subpixel voltage and a thirdsubpixel voltage defined as the third voltage relative to the commonvoltage may be in a range of about 60-95% of an absolute magnitude ofthe first subpixel voltage.

The second and the third subpixel electrodes may occupy an area equal toor smaller than about 80% of an area of the pixel electrode.

A ratio of an area of each of the second and the third subpixelelectrodes relative to an area of the first subpixel electrode may beabout 1-5.

The liquid crystal display may further include a coupling electrodeconnected to the first subpixel electrode and overlapping the second andthe third subpixel electrodes for forming the capacitive coupling.

The coupling electrode may have first and second portions overlappingthe second and the third subpixel electrodes, respectively, and thefirst and the second portions of the coupling electrode may havedifferent widths.

Overlapping areas between the coupling electrode and the second and thethird subpixel electrodes may be different.

The liquid crystal display may further include a fourth subpixelelectrode capacitively coupled with the first to the third subpixelelectrodes and having a fourth voltage.

Relative value of a sum of the first subpixel voltage and the thirdsubpixel voltage and a sum of the second subpixel voltage and a fourthsubpixel voltage defined as the fourth voltage relative to the commonvoltage may be in a range of about 80-100%.

The liquid crystal display may further include a coupling electrodeconnected to the first subpixel electrode and overlapping the second tothe fourth subpixel electrodes for forming the capacitive coupling.

The coupling electrode may have first to third portions overlapping thesecond to the fourth subpixel electrodes, respectively, and the first tothe third portions of the coupling electrode may have different widths.

Overlapping areas between the coupling electrode and the second to thefourth subpixel electrodes may be different.

The second signal line may include a curved portion including at leasttwo rectilinear portions alternately arranged with making clockwise andcounterclockwise angles with the first signal line.

The pixel electrode may have a shape of curved stripes that is curved atleast twice and the first subpixel electrode and the second subpixelelectrode may be divided at curved portions of the pixel electrode.

The pixel electrode and the common electrode may include a tiltdirection determining member curved following the shape of the pixelelectrode.

The liquid crystal display may further include a storage electrode linethat extends substantially parallel to the first signal line andincludes a storage electrode overlapping the pixel electrode.

A liquid crystal display is provided, which includes: a first panelincluding a first signal line, a second signal line intersecting thefirst signal line, a thin film transistor connected to the first and thesecond signal lines, and a pixel electrode connected to the thin filmtransistor and including a first subpixel electrode and a plurality ofsecond subpixel electrodes separated from each other and capacitivelycoupled to the first subpixel electrode; a second panel including acommon electrode facing the pixel electrode and supplied with a commonvoltage; and a vertically aligned liquid crystal layer that isinterposed between the pixel electrode and the common electrode, whereinthe first and the second subpixel electrodes have first and secondsubpixel voltages relative to the common voltage and the second subpixelvoltages have different voltage ratios with respect to the firstsubpixel voltage.

An absolute magnitude of each of the second subpixel voltages may belower than an absolute magnitude of the first subpixel voltage.

The number of the second subpixel electrodes may be two.

The first subpixel electrode may have an area equal to or smaller thanan area of the second subpixel electrodes.

The absolute magnitude of each of the second subpixel voltages may be ina range of about 60-95% of an absolute magnitude of the first subpixelvoltage.

The second subpixel electrodes may occupy an area equal to or smallerthan about 80% of an area of the pixel electrode.

A ratio of an area of each of the second subpixel electrodes relative toan area of the first subpixel electrode may be about 1-5.

The liquid crystal display may further include a coupling electrodeconnected to the first subpixel electrode and overlapping the secondsubpixel electrodes for forming the capacitive coupling.

The coupling electrode may have a plurality of portions overlapping thesecond subpixel electrodes, respectively, and having different widths.

Overlapping areas between the coupling electrode and the second subpixelelectrodes may be different.

The number of the second subpixel electrode may be three.

The liquid crystal display may further include a coupling electrodeconnected to the first subpixel electrode and overlapping the secondsubpixel electrodes for forming the capacitive coupling.

The coupling electrode may have a plurality of portions overlapping thesecond subpixel electrodes, respectively, and having different widths.

Overlapping areas between the coupling electrode and the second subpixelelectrodes may be different.

A liquid crystal display is provided, which includes: a first panelincluding a first signal line, a second signal line intersecting thefirst signal line, a thin film transistor connected to the first and thesecond signal lines, and a pixel electrode connected to the thin filmtransistor and including a plurality of subpixel electrodes separatedfrom each other; a second panel including a common electrode facing thepixel electrode and supplied with a common voltage; and a verticallyaligned liquid crystal layer that is interposed between the pixelelectrode and the common electrode, wherein the subpixel electrodes havedifferent voltages and one of the second subpixel electrodes having ahigher voltage has an area equal to or smaller than another of thesecond subpixel electrodes having a lower voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more apparent by describingembodiments thereof in detail with reference to the accompanyingdrawings in which:

FIG. 1 is a layout view of a TFT array panel for an LCD according to anembodiment of the present invention;

FIG. 2 is a layout view of a common electrode panel for an LCD accordingto an embodiment of the present invention;

FIG. 3 is a layout view of an LCD including the TFT array panel shown inFIG. 1 and the common electrode panel shown in FIG. 2;

FIGS. 4 and 5 are sectional views of the LCD shown in FIG. 3 taken alongthe lines IV-IV′ and V-V′, respectively;

FIG. 6 is an equivalent circuit diagram of the LCD shown in FIGS. 1-5;

FIG. 7 is a layout view of an LCD according to another embodiment of thepresent invention;

FIG. 8 is a layout view of an LCD according to another embodiment of thepresent invention;

FIG. 9 is a sectional view of the LCD shown in FIG. 8 taken along theline IX-IX′; and

FIGS. 10 and 11 are graphs illustrating light transmittance of the LCDshown in FIGS. 7 and 3, respectively, as well as light transmittance ofa conventional vertically aligned mode LCD as function of voltageapplied to a liquid crystal layer.

DETAILED DESCRIPTION OF EMBODIMENTS

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. The present invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein.

In the drawings, the thickness of layers, films and regions areexaggerated for clarity. Like numerals refer to like elementsthroughout. It will be understood that when an element such as a layer,film, region or substrate is referred to as being “on” another element,it can be directly on the other element or intervening elements may alsobe present. In contrast, when an element is referred to as being“directly on” another element, there are no intervening elementspresent.

Now, liquid crystal displays according to embodiments of the presentinvention will be described with reference to the accompanying drawings.

An LCD according to an embodiment of the present invention is describedin detail with reference to FIGS. 1-5.

FIG. 1 is a layout view of a TFT array panel for an LCD according to anembodiment of the present invention, FIG. 2 is a layout view of a commonelectrode panel for an LCD according to an embodiment of the presentinvention, FIG. 3 is a layout view of an LCD including the TFT arraypanel shown in FIG. 1 and the common electrode panel shown in FIG. 2,and FIGS. 4 and 5 are sectional views of the LCD shown in FIG. 3 takenalong the lines IV-IV′ and V-V′, respectively.

An LCD according to an embodiment of the present invention includes aTFT array panel 100, a common electrode panel 200 facing the TFT arraypanel 100, and a LC layer 3 interposed between the TFT array panel 100and the common electrode panel 200.

The TFT array panel 100 is now described in detail with reference toFIGS. 1 and 3-5.

A plurality of gate lines 121 and a plurality of pairs of storageelectrode lines 131 a and 131 b are formed on an insulating substrate110.

The gate lines 121 for transmitting gate signals extend substantially ina transverse direction and are separated from each other. Each gate line121 includes a plurality of projections forming a plurality of gateelectrodes 124. The gate lines 121 may extend to be connected to adriving circuit (not shown) integrated on the substrate 110, or it mayhave an end portion (not shown) having a large area for connection withanother layer or an external driving circuit mounted on the substrate110 or on another device such as a flexible printed circuit film (notshown) that may be attached to the substrate 110.

The storage electrode lines 131 a and 131 b extend substantially in thetransverse direction, but they are curved near the gate electrodes 124.Each pair of the storage electrode lines 131 a and 131 b include aplurality of pairs of storage electrodes 133 a and 133 b that areconnected thereto and extend parallel to each other. Each storageelectrode 133 a or 133 b is three times curved with a substantiallyright angle such that it includes four oblique portions making an angleof about 45 degrees with the gate lines 121 and connected in turn with asubstantially right angle. The storage electrode lines 131 a and 131 bare supplied with a predetermined voltage such as a common voltage,which is applied to a common electrode 270 on the common electrode panel200 of the LCD.

The gate lines 121 and the storage electrode lines 131 a and 131 b arepreferably made of Al containing metal such as Al and Al alloy, Agcontaining metal such as Ag and Ag alloy, Cu containing metal such as Cuand Cu alloy, Mo containing metal such as Mo and Mo alloy, Cr, Ta, orTi. However, they may have a multi-layered structure including two filmshaving different physical characteristics. One of the two films ispreferably made of low resistivity metal including Al containing metal,Ag containing metal, or Cu containing metal for reducing signal delay orvoltage drop in the gate lines 121 and the storage electrode lines 131 aand 131 b. On the other hand, the other film is preferably made ofmaterial such as Cr, Mo, Mo alloy, Ta, or Ti, which has good physical,chemical, and electrical contact characteristics with other materialssuch as indium tin oxide (ITO) or indium zinc oxide (IZO). Goodexemplary combination of the two film materials are a pair of a lower Crfilm and an upper Al (alloy) film and a pair of a lower Al (alloy) filmand a Mo (alloy) film.

In addition, the lateral sides of the gate lines 121 and the storageelectrode lines 131 a and 131 b are inclined relative to a surface ofthe substrate 110, and the inclination angle thereof ranges about 30-80degrees.

A gate insulating layer 140 preferably made of silicon nitride (SiNx) isformed on the gate lines 121 and the storage electrode lines 131 a and131 b.

A plurality of semiconductor stripes 151 preferably made of hydrogenatedamorphous silicon (abbreviated as “a-Si”) or polysilicon are formed onthe gate insulating layer 140. Each semiconductor stripe 151 extendssubstantially parallel to the storage electrodes 133 a and 133 b suchthat it is curved periodically. Each semiconductor stripe 151 has aplurality of projections 154 branched out toward the gate electrodes 124and the width of each semiconductor stripe 151 becomes large near thegate lines 121 and the storage electrode lines 131 a and 131 b such thatthe semiconductor stripe 151 covers large areas of the gate lines 121and the storage electrode lines 131 a and 131 b.

A plurality of ohmic contact stripes and islands 161 and 165 preferablymade of silicide or n+hydrogenated a-Si heavily doped with n typeimpurity are formed on the semiconductor stripes 151. Each ohmic contactstripe 161 has a plurality of projections 163, and the projections 163and the ohmic contact islands 165 are located in pairs on theprojections 154 of the semiconductor stripes 151.

The lateral sides of the semiconductor stripes 151 and the ohmiccontacts 161 and 165 are inclined relative to the surface of thesubstrate 110, and the inclination angles thereof are preferably in arange of about 30-80 degrees.

A plurality of data lines 171 and a plurality of drain electrodes 175separated from each other are formed on the ohmic contacts 161 and 165and the gate insulating layer 140.

The data lines 171 for transmitting data voltages extend substantiallyin the longitudinal direction and intersect the gate lines 121 and thestorage electrode lines 131 a and 131 b. Each data line 171 has an endportion 179 having a large area for contact with another layer or anexternal device and it includes a plurality of curved portions and aplurality of longitudinal portions such that it curves periodically.Each curved portion includes four oblique portions connected in turn toform a letter “W” and opposite ends of the curved portion are connectedto respective longitudinal portions. The oblique portions of the datalines 171 make an angle of about 45 degrees with the gate lines 121, andthe longitudinal portions cross over the gate electrodes 124. The lengthof a curved portion is about one to nine times the length of alongitudinal portion, that is, it occupies about 50-90 percents of thetotal length of the curved portion and the longitudinal portion.

Each drain electrode 175 includes a thin film transistor (TFT) portionand a coupling electrode 176 connected thereto. The TFT portion of thedrain electrode 175 obliquely extends from a linear end portion disposednear a gate electrode 124 to an expansion having a large area forcontact with another layer. The expansion of the drain electrode 175 hasa chamfered corner substantially parallel to the storage electrodes 133a and 133 b. Each longitudinal portion of the data lines 171 includes aplurality of projections such that the longitudinal portion includingthe projections forms a source electrode 173 partly enclosing a linearend portion of a TFT portion of a drain electrode 175. Each set of agate electrode 124, a source electrode 173, and a drain electrode 175along with a projection 154 of a semiconductor stripe 151 form a TFThaving a channel formed in the semiconductor projection 154 disposedbetween the source electrode 173 and the drain electrode 175.

Each coupling electrode 176 of a drain electrode 175 is connected to theexpansion of the drain electrode 175. The coupling electrode 176 isdisposed between a pair of storage electrodes 133 a and 133 b andequidistant from the pair of storage electrodes 133 a and 133 b, and itextends substantially parallel to the storage electrodes 133 a and 133 bsuch that it has three curve points, i.e., lower, middle, and uppercurve points getting away from the expansion of the drain electrode 175.The width a, b and c of the coupling electrode 176 may be different fromeach other and ranges preferably about 3-15 microns. The couplingelectrode 176 includes a pair of transverse branches 177 extending frommiddle and upper curve points of the coupling electrode 176 and makingan obtuse angle with other portions of the coupling electrode 176.

The data lines 171 and the drain electrodes 175 are preferably made ofrefractory metal such as Cr, Mo, Mo alloy, Ta and Ti. They may also havea multi-layered structure including a refractory metal film (not shown)and a low-resistivity film (not shown). A good example of thecombination is a lower Mo (alloy) film, an intermediate Al (alloy) film,and an upper Mo (alloy) film as well as the above-described combinationsof a lower Cr film and an upper Al (alloy) film and a lower Al (alloy)film and an upper Mo (alloy) film.

Like the gate lines 121 and the storage electrode lines 131 a and 131 b,the data lines 171 and the drain electrodes 175 have inclined lateralsides with respect to the surface of the substrate 110, and theinclination angles thereof range about 30-80 degrees.

The ohmic contacts 161 and 165 are interposed only between theunderlying semiconductor stripes 151 and the overlying data lines 171and the overlying drain electrodes 175 thereon and reduce the contactresistance therebetween. The semiconductor stripes 151 include aplurality of exposed portions, which are not covered with the data lines171 and the drain electrodes 175, such as portions located between thesource electrodes 173 and the drain electrodes 175. Although thesemiconductor stripes 151 are narrower than the data lines 171 at mostplaces, the width of the semiconductor stripes 151 becomes large nearthe gate lines 121 and the storage electrode lines 131 a and 131 b asdescribed above, to smooth the profile of the surface, therebypreventing the disconnection of the data lines 171.

A passivation layer 180 is formed on the data lines 171, the drainelectrodes 175, and exposed portions of the semiconductor stripes 151,which are not covered with the data lines 171 and the drain electrodes175. The passivation layer 180 is preferably made of low dielectricinsulating material such as a-Si:C:O and a-Si:O:F formed by plasmaenhanced chemical vapor deposition (PECVD), organic insulator orinorganic insulator such as silicon nitride and silicon oxide. Thepassivation layer 180 may have a double-layered structure including alower inorganic film and an upper organic film in order to prevent thechannel portions of the semiconductor stripes 151 from being in directcontact with organic material. The passivation layer 180 may have aposition-dependent thickness.

The passivation layer 180 has a plurality of contact holes 182 and 185exposing the end portions 179 of the data lines 171 and the drainelectrodes 175, respectively. The passivation layer 180 and the gateinsulating layer 140 have a plurality of contact holes 184 exposing thestorage electrode lines 131 a and 131 b. The contact holes 182, 184 and185 can have various shapes such as polygon or circle. The sidewalls ofthe contact holes 182, 184 and 185 are inclined with an angle of about30-85 degrees or have stepwise profiles.

A plurality of pixel electrodes 190 including first to third subpixelelectrodes 190 a-190 c, a plurality of contact assistants 82, and aplurality of storage overpasses 84, which are preferably made of ITO orIZO, are formed on the passivation layer 180.

Each pixel electrode 190 is located substantially in an area enclosed bythe data lines 171 and the gate lines 121, and it has a pair oftransverse edges extending substantially parallel to the storageelectrode lines 131 a and 131 b and a pair of curved edges substantiallyparallel to the data lines 171 such that it also forms a letter “W.”

The subpixel electrodes 190 a-190 c are divided by a pair of gaps 194extending in the transverse direction from the lower and the upper curvepoints of a data line 171 such that the first and the third subpixelelectrodes 190 a and 190 c are nearly parallelogrammic and the secondpixel electrode 190 b has a shape of chevron. However, the pixelelectrodes 190 may be divided into a plurality of subpixel electrodeshaving various shapes and for example, the pixel electrodes 190 may bedivided by a curved gap overlapping the coupling electrodes 176.

The first subpixel electrode 190 is physically and electricallyconnected to a drain electrode 175 through a contact hole 185 such thatthe first subpixel electrode 190 a receives the data voltages from thedrain electrode 175.

The second and the third subpixel electrodes 190 b and 190 c overlap acoupling electrode 176 to be capacitively coupled with the firstsubpixel electrode 190 a. The second subpixel electrode 190 b has atransverse cutout 193 extending from a concave vertex thereof. Theposition-dependent thickness of the passivation layer 180 and theposition-dependent width of the coupling electrode 176 may differentiatethe coupling capacitance between the first subpixel electrode 190 a andthe second and the third subpixel electrodes 190 b and 190 c.

The subpixel electrodes 190 a-190 c supplied with the data voltages orthe voltages obtained by the capacitive coupling generate electricfields in cooperation with the common electrode 270, which determineorientations of liquid crystal molecules 310 disposed therebetween.

A subpixel electrode 190 a-190 c and the common electrode 270 form acapacitor called a “liquid crystal capacitor,” which stores appliedvoltages after turn-off of the TFT. An additional capacitor called a“storage capacitor,” which is connected in parallel to the liquidcrystal capacitor, is provided for enhancing the voltage storingcapacity. The storage capacitors are implemented by overlapping thesubpixel electrodes 190 a-190 c with the storage electrode lines 131 aand 131 b including the storage electrodes 133 a and 133 b.

The contact assistants 82 are connected to the exposed end portions 179of the data lines 171 through the contact holes 182. The contactassistants 82 protect the exposed end portions 179 and complement theadhesion between the exposed end portions 179 and external devices. Thecontact assistants 82 may be omitted when the end portions 179 areomitted.

The storage overpasses 84 cross over the gate lines 121 and they areconnected to a pair of the storage electrode lines 131 through thecontact holes 184 disposed opposite each other with respect to the gatelines 121.

Finally, an alignment layer 11 that may be homeotropic is formed on thepixel electrodes 190, the contact assistants 82, the storage overpasses84, and the passivation layer 180.

The description of the common electrode panel 200 follows with referenceto FIGS. 2-4.

A light blocking member 220 called a black matrix is formed on aninsulating substrate 210 such as transparent glass and it may include aplurality of curved portions facing the curved portions of the datalines 171 and a plurality of expanded portions facing the TFTs and thelongitudinal portions of the data lines 171 such that the light blockingmember 220 prevents light leakage between the pixel electrodes 190 anddefines open areas facing the pixel electrodes 190.

A plurality of color filters 230 are formed on the substrate 210 and thelight blocking member 220 and each of the color filters 230 is disposedsubstantially in the open areas defined by the light blocking member220. The color filters 230 disposed between adjacent two data lines 171and arranged in the longitudinal direction may be connected to eachother to form a stripe. Each color filter 230 may represent one of threeprimary colors such as red, green and blue colors. The color filters 230may be disposed on the TFT array panel 100, and in this case, they maybe disposed under the gate insulating layer 140 or under the passivationlayer 180.

An overcoat 250 preferably made of silicon nitride or organic materialis formed on the color filters 230 and the light blocking member 220.The overcoat 250 protects the color filters 230 and gives a flat topsurface.

A common electrode 270 preferably made of transparent conductivematerial such as ITO and IZO is formed on the overcoat 250. The commonelectrode 270 is supplied with the common voltage and it has a pluralityof W-shaped cutouts 271 facing respective pixel electrodes 190.

The cutout 271 includes a curved portion that overlaps a couplingelectrode 176 and has three curve points, three intermediate transverseportions 274 that extend from the curve points and make obtuse angleswith the curved portion, and a pair of terminal transverse portions 272that are connected to respective ends of the curved portion and makeobtuse angles with the curved portion.

The curved portion of the cutout 271 may bisect the partitions of thepixel electrode 190 into left and right halves, and they have fourrectilinear oblique portions that are connected in turn and have pairsof concave notches 273. Each pair of notches 273 face each other anddisposed near a center of a rectilinear oblique portion.

The transverse portions 274 of the cutout 271 include a lower transverseportion disposed between the first subpixel electrode 190 a and thesecond subpixel electrode 190 b, a middle transverse portion overlappingthe second subpixel electrode 190 b and a transverse branch of acoupling electrode 176 and forming a line with a cutout of the secondsubpixel electrode 190 b, and an upper transverse portion disposedbetween the second subpixel electrode 190 b and the third subpixelelectrode 190 c and overlapping another transverse branch of thecoupling electrode 176. The transverse portions 274 have differentwidths as shown in FIGS. 2 and 3 such that the subpixel electrodes 190a-190 c have different overlapping areas with the common electrode 270although it is optional.

The terminal transverse portions 274 of the cutout 271 are aligned withtransverse edges of the pixel electrode 190, respectively. The cutout271/272 preferably has a width W in a range of about 6-20 microns.

The light blocking member 220 may also overlap the cutouts 271 and 272to block the light leakage through the cutouts 271 and 272.

A homeotropic alignment layer 21 is coated on the common electrode 270.

The alignment layers 11 and 21 may be homogeneous alignment layers.

A pair of polarizers 12 and 22 are provided on outer surfaces of thepanels 100 and 200 such that their transmissive axes are crossed and oneof the transmissive axes is parallel to the gate lines 121. In addition,a retardation film 13/23 for compensating the retardation of the LClayer 3 is disposed between the polarizer 12/23 and the outer surface ofthe panel 100/200.

The LCD may further include a backlight unit for providing light for theLCD.

The LC layer 3 has negative dielectric anisotropy and the LC molecules310 in the LC layer 3 are aligned such that their long axes are verticalto the surfaces of the panels 100 and 200 in absence of electric field.

Upon application of the common voltage to the common electrode 270 and adata voltage to the pixel electrodes 190, a primary electric fieldsubstantially perpendicular to the surfaces of the panels 100 and 200 isgenerated. The LC molecules 310 tend to change their orientations inresponse to the electric field such that their long axes areperpendicular to the field direction. In the meantime, the cutouts 271and 272 of the pixel electrodes 190 and the common electrode 270 and theoblique edges of the pixel electrodes 190 distort the primary electricfield to have a horizontal component which determines the tiltdirections of the LC molecules 310. The horizontal component of theprimary electric field is perpendicular to the edges of the cutouts 271and 272 and the oblique edges of the pixel electrodes 190. Thehorizontal component of the primary field varies depending on positionson a pixel electrode 190.

Accordingly, several sub-regions having different tilt directions, whichare partitioned by outer edges of a pixel electrode 190, a cutout 271 ofthe common electrode 270, the gaps 194, and the transverse portions 177,and a cutout 193 of the pixel electrode 190, are formed in a pixelregion of the LC layer 3, which are located on the pixel electrode 190.Each sub-region has two major edges defined by the cutout 271 and anoblique outer edge of the pixel electrodes 190 a and 190 b,respectively. The sub-regions are classified into a plurality of,preferably four, domains based on the tilt directions.

In the meantime, the direction of a secondary electric field due to thevoltage difference between the pixel electrodes 190 is perpendicular tothe edges of the pixel electrodes and the cutouts 191, 271 and 272.Accordingly, the field direction of the secondary electric fieldcoincides with that of the horizontal component of the primary electricfield in the primary domains. Consequently, the secondary electric fieldbetween the pixel electrodes 190 enhances the determination of the tiltdirections of the LC molecules 310 in the primary domains.

Meanwhile, the transverse portions 177 of the coupling electrode 176block the light leakage between the subpixel electrodes 190 b and 190 cand the notches 173 may give stable alignment near the boundaries of thesub-regions, thereby preventing spots or afterimages near the boundariesof the sub-regions.

Since the LCD performs inversion such as dot inversion, columninversion, etc., adjacent pixel electrodes are supplied with datavoltages having opposite polarity with respect to the common voltage andthus a secondary electric field between the adjacent pixel electrodes isalmost always generated to enhance the stability of the primary domains.

Since the tilt directions of all domains make an angle of about 45degrees with the gate lines 121, which are parallel to or perpendicularto the edges of the panels 100 and 200, and the 45-degree intersectionof the tilt directions and the transmissive axes of the polarizers givesmaximum transmittance, the polarizers can be attached such that thetransmissive axes of the polarizers are parallel to or perpendicular tothe edges of the panels 100 and 200 and it reduces the production cost.

The number, shapes, and arrangements of the cutouts 271 and the gaps 194may be modified depending on the design factors. Moreover, the cutouts271 may be substituted with protrusions, preferably made of organicmaterial, and preferably having width ranging about 5-15 microns.

The LCD shown in FIGS. 1-5 is represented as an equivalent circuit shownin FIG. 6.

Referring to FIG. 6, the LCD includes a plurality of gate lines G, aplurality of data lines D, and a plurality of pixels, and each pixelincludes first to third subpixels including first to third LC capacitorsC_(LC)a-C_(LC)C, two coupling capacitors Ccp1 and Ccp2, a storagecapacitor Cst, and a TFT Q. The TFT Q has a control terminal (gateelectrode) connected to a gate line G, an input terminal (sourceelectrode) connected to a data line D, and an output terminal (drainelectrode) connected to the first LC capacitor C_(LC)a, a storagecapacitor Cst, and the coupling capacitors Ccp1 and Ccp2. The couplingcapacitors Ccp1 and Ccp2 are connected between the TFT Q and the secondand the third LC capacitors C_(LC)b and C_(LC)c. The first/second/thirdLC capacitor C_(LC)a/C_(LC)b/C_(LC)c is formed of a first/second/thirdsubpixel electrode 190 a/190 b/190 c, a common electrode 270, and aregion of a LC layer 300 disposed on the first/second/third pixelelectrode 190 a/190 b/190 c. The storage capacitor Cst is formed of thepixel electrode 190, a storage electrode line 131, and insulator(s) 140and 180 interposed therebetween. The coupling capacitor Ccp1/Ccp2 isformed of a coupling electrode 176, the second/third subpixel electrode190 b/190 c, and an insulator 140 interposed therebetween.

Since the second and the third LC capacitors C_(LC)b and C_(LC)c arecoupled with the TFT Q or the first subpixel electrode 190 a through thecoupling capacitors Ccp1 and Ccp2, they are supplied with voltagesdifferent from a voltage applied to the first subpixel electrode 190 a.The voltage of each of the second and the third LC capacitors C_(LC)band C_(LC)c are lower than the voltage of the first LC capacitorC_(LC)a. This configuration reduces the distortion of a gamma curve ofthe LCD. The voltage of the second or the third LC capacitors C_(LC)band C_(LC)c are adjusted by varying the overlapping areas between thecoupling electrode 176 and the second or the third subpixel electrodes190 b or 190 c, and preferably about 0.95-0.60 of that of the first LCcapacitor C_(LC)a.

In addition, one of the three subpixel electrodes 190 a-190 c having ahigher voltage preferably has an area equal to or smaller than anotherof the three subpixel electrodes 190 a-190 c having a lower voltage.

According to a simulation, it is preferable that the area of the firstsubpixel electrode 190 a is equal to or smaller than about half of thearea of the second and the third subpixel electrodes 190 b and 190 c,and the gap 194 has a width of about 2-5 microns. It is preferable thatthe area of the second and the third subpixel electrodes 190 b and 190 cis equal to or smaller than about 80% of the pixel electrode 190, and anabsolute magnitude of a voltage of the second and the third LCcapacitors C_(LC)b and C_(LC)c is in a range of about 60-95% of anabsolute magnitude of the voltage of the first LC capacitor C_(LC)a. Inaddition, areal ratios of the second and the third subpixel electrodes190 b and 190 c are about 1:1 to 1:5.

Now, the reason why the capacitive coupling makes the magnitude of thevoltages of the second and the third LC capacitors C_(LC)b and C_(LC)clower than that of the first pixel electrode 190 a, which will bedescribed in detail.

The voltage across the first, the second, and the third LC capacitorsC_(LC)a, C_(LC)b and C_(LC)c is denoted by Va, Vb and Vc, respectively.The voltage distribution law results in:Vb=Va×[Ccp 1/(Ccp+C _(LC) b)]; andVc=Va×[Ccp 2/(Ccp 1+C _(LC) b+Ccp 2+C _(LC) c)].

Since Ccp1/(Ccp+C_(LC)b) and Ccp1/(Ccp1+C_(LC)b+Ccp2+C_(LC)c) is smallerthan one, the voltages Vb and Vc is smaller than the voltage Va.

An LCD according to another embodiment of the present invention will bedescribed in detail with reference to FIG. 7 as well as FIGS. 2-5.

FIG. 7 is a layout view of an LCD according to another embodiment of thepresent invention.

An LCD according to this embodiment includes a TFT array panel shown inFIG. 7, a common electrode panel 200 shown in FIG. 2, and a LC layer 3interposed therebetween. The sectional views of FIGS. 4 and 5 may beapplicable to the LCD shown in FIG. 7 with a little exception.

Layered structures of the panels 100 and 200 according to thisembodiment are almost the same as those shown in FIGS. 1-5.

Regarding the TFT array panel 100, a plurality of gate lines 121including a plurality of gate electrodes 124 and a plurality of storageelectrode lines 131 a and 131 b including a plurality of storageelectrodes 133 a and 133 b are formed on a substrate 110, and a gateinsulating layer 140, a plurality of semiconductor stripes 151 includinga plurality of projections 154, and a plurality of ohmic contact stripes161 including a plurality of projections 163 and a plurality of ohmiccontact islands 165 are sequentially formed thereon. A plurality of datalines 171 including a plurality of source electrodes 173 and a pluralityof drain electrodes 175 are formed on the ohmic contacts 161 and 165,and a passivation layer 180 is formed thereon. A plurality of contactholes 182, 184 and 185 are provided at the passivation layer 180 and thegate insulating layer 140. A plurality of pixel electrodes 190, aplurality of storage overpasses 84, and a plurality of contactassistants 82 are formed on the passivation layer 180 and an alignmentlayer 11 is coated thereon. The storage electrodes 133 a and 133 b arethrice curved and the data lines 171 include a plurality of curvedportions, each curved portion being thrice curved. In addition, eachpixel electrode 190 has two curved edges that extend substantiallyparallel to each other and are thrice curved to have lower, middle, andupper curve points.

Regarding the common electrode panel 200, a light blocking member 220, aplurality of color filters 230, an overcoat 250, a common electrode 270having cutouts 271 that includes lower, middle, and upper transverseportions 274, and an alignment layer 21 are formed on an insulatingsubstrate 210.

Different from the LCD shown in FIGS. 1-5, each pixel electrode 190includes two chevron-shaped subpixel electrodes 190 d and 190 e dividedby a gap 194 passing through the middle curve points of the curvededges. Each subpixel electrode 190 d or 190 e has a transverse cutout193 extending from a concave vertex thereof and forming a line with atransverse portion 274 of the cutout 271 of the common electrode 270.

Many of the above-described features of the LCD shown in FIGS. 1-5 maybe appropriate to the LCD shown in FIG. 7.

An LCD according to another embodiment of the present invention will bedescribed in detail with reference to FIGS. 8 and 9.

FIG. 8 is a layout view of an LCD according to another embodiment of thepresent invention, and FIG. 9 is a sectional view of the LCD shown inFIG. 8 taken along the line IX-IX′.

Referring to FIGS. 8 and 9, an LCD according to this embodiment includesa TFT array panel 100, a common electrode panel 200, and a LC layer 3interposed therebetween.

Layered structures of the panels 100 and 200 according to thisembodiment are almost the same as those shown in FIGS. 1-5.

Regarding the TFT array panel 100, a plurality of gate lines 121including a plurality of gate electrodes 124 and a plurality of storageelectrode lines 131 a and 131 b including a plurality of storageelectrodes 133 a and 133 b are formed on a substrate 110, and a gateinsulating layer 140, a plurality of semiconductor stripes 151 includinga plurality of projections 154, and a plurality of ohmic contact stripes161 including a plurality of projections 163 and a plurality of ohmiccontact islands 165 are sequentially formed thereon. A plurality of datalines 171 including a plurality of source electrodes 173 and a pluralityof drain electrodes 175 are formed on the ohmic contacts 161 and 165,and a passivation layer 180 is formed thereon. A plurality of contactholes 182, 184 and 185 are provided at the passivation layer 180 and thegate insulating layer 140. A plurality of pixel electrodes 190, aplurality of storage overpasses 84, and a plurality of contactassistants 82 are formed on the passivation layer 180 and an alignmentlayer 11 is coated thereon. The storage electrodes 133 a and 133 b arethrice curved and the data lines 171 include a plurality of curvedportions, each curved portion being thrice curved. In addition, eachpixel electrode 190 has two curved edges that extend substantiallyparallel to each other and are thrice curved to have lower, middle, andupper curve points.

Regarding the common electrode panel 200, a light blocking member 220, aplurality of color filters 230, an overcoat 250, a common electrode 270having cutouts 271 that includes lower, middle, and upper transverseportions 274, and an alignment layer 21 are formed on an insulatingsubstrate 210.

Different from the LCD shown in FIGS. 1-5, each pixel electrode 190includes first to fourth parallelogrammic subpixel electrodes 190 f-190i divided by three gaps 194 passing through the opposite curve points ofthe curved edges.

The subpixel electrodes 190 f-190 i and the common electrode 190 formrespective LC capacitors and it is preferable that the sum of thevoltages across the LC capacitors formed by the first and the thirdsubpixel electrodes 190 f and 190 g is the same as that by the secondand the fourth subpixel electrodes 190 g and 190i. It is preferable thatthe latter to former or the former to the latter is about 80-100%. Thevoltages of the LC capacitors formed by the first to the third subpixelelectrodes 190 a-190 c may be decreasing from the first subpixelelectrode 190 a and to the third subpixel electrode 190 c.

In addition, the semiconductor stripes 151 have almost the same planarshapes as the data lines 171 and the drain electrodes 175 as well as theunderlying ohmic contacts 161 and 165. However, the projections 154 ofthe semiconductor stripes 151 include some exposed portions, which arenot covered with the data lines 171 and the drain electrodes 175, suchas portions located between the source electrodes 173 and the drainelectrodes 175.

A manufacturing method of the TFT array panel according to an embodimentsimultaneously forms the data lines 171, the drain electrodes 175, thesemiconductors 151, and the ohmic contacts 161 and 165 using onephotolithography process.

A photoresist pattern for the photolithography process hasposition-dependent thickness, and in particular, it has first and secondportions with decreased thickness. The first portions are located onwire areas that will be occupied by the data lines 171 and the drainelectrodes 175 and the second portions are located on channel areas ofTFTs.

The position-dependent thickness of the photoresist is obtained byseveral techniques, for example, by providing translucent areas on theexposure mask as well as transparent areas and light blocking opaqueareas. The translucent areas may have a slit pattern, a lattice pattern,a thin film(s) with intermediate transmittance or intermediatethickness. When using a slit pattern, it is preferable that the width ofthe slits or the distance between the slits is smaller than theresolution of a light exposer used for the photolithography. Anotherexample is to use reflowable photoresist. In detail, once a photoresistpattern made of a reflowable material is formed by using a normalexposure mask only with transparent areas and opaque areas, it issubject to reflow process to flow onto areas without the photoresist,thereby forming thin portions.

As a result, the manufacturing process is simplified by omitting aphotolithography step.

Many of the above-described features of the LCD shown in FIGS. 1-5 maybe appropriate to the LCD shown in FIGS. 6-8.

Referring to FIGS. 10 and 11, the advantages of the LCDs according tothe embodiments of the present invention will be described in detail.

FIGS. 10 and 11 are graphs illustrating light transmittance of the LCDshown in FIGS. 7 and 3, respectively, as well as light transmittance ofa conventional vertically aligned mode LCD as function of voltageapplied to a liquid crystal layer.

In FIGS. 10 and 11, “#1” represents a transmittance curve for aconvention LCD, and “#2” represents a transmittance curve for an LCDshown in FIG. 7 or 3.

As shown in FIGS. 10 and 11, the conventional LCD shows a steep curve(#1) and thus a deviation of a voltage applied to a pixel electrode fora low gray may steep variation of the light transmittance, therebydecreasing image quality. For example, driving circuit integratedcircuits (IC) having little output deviations may cause voltagedeviation for a given gray such that longitudinal stripes may appear inthe LCD.

However, the curves (#2) shown in FIGS. 10 and 11 have smooth steepnesssuch that the light transmittance may not be abruptly varied dependingon the voltage particularly for low grays, thereby improving visibilityof the LCD.

When a “steepness” of a transmittance curve is defined as a gradientbetween the light transmittance of 5.5% and 1.5%, i.e.,(5.5%-1.5%)/(V(5.5%)-V(1.5%)) and it is preferable that the steepness ofan LCD is lower than 20. The light transmittance in a range of about5.5-1.5% is most sensitively recognized by human eyes and the variationof the light transmittance in this range due to the output deviation ofthe data driving IC is easily perceived as longitudinal or transversestripes.

For an LCD shown in FIG. 7, when the ratio of the area between the firstsubpixel electrode 190 a and the second subpixel electrode 190 b is 1:1and the ratio of the voltage across the liquid crystal capacitors formedby the first subpixel electrode 190 a and the second subpixel electrode190 b is 1:0.7, the steepness was measured to be about 16, which islower than 20.

For an LCD shown in FIG. 3, when the ratio of the area of the first, thesecond, and the third subpixel electrodes 190 a, 190 b and 190 c is1:2:1 and the ratio of the voltage across the liquid crystal capacitorsformed by the first, the second, and the third subpixel electrodes 190a, 190 b and 190 c is 1:0.7:0.65, the steepness was measured to be about11.5, which is very slow.

While the present invention has been described in detail with referenceto the preferred embodiments, those skilled in the art will appreciatethat various modifications and substitutions can be made thereto withoutdeparting from the spirit and scope of the present invention as setforth in the appended claims.

1. A liquid crystal display comprising: a first panel including a firstsignal line, a second signal line intersecting the first signal line, athin film transistor connected to the first and the second signal lines,and a pixel electrode connected to the thin film transistor andincluding a first subpixel electrode having a first voltage and a secondsubpixel electrode capacitively coupled to the first subpixel electrodeand having a second voltage; a second panel including a common electrodefacing the pixel electrode and supplied with a common voltage; and avertically aligned liquid crystal layer that is interposed between thepixel electrode and the common electrode, wherein a steepness of lighttransmittance as function of a voltage applied the first subpixelelectrode with respect to the common voltage is lower than about
 20. 2.The liquid crystal display of claim 1, wherein an absolute magnitude ofa first subpixel voltage defined as the first voltage relative to thecommon voltage is higher than an absolute magnitude of a second subpixelvoltage defined as the second voltage relative to the common voltage. 3.The liquid crystal display of claim 2, further comprising a thirdsubpixel electrode capacitively coupled to the first and the secondsubpixel electrodes and having a third voltage.
 4. The liquid crystaldisplay of claim 3, wherein an area of the first subpixel electrode isequal to or smaller than half of an area of the second and the thirdsubpixel electrodes.
 5. The liquid crystal display of claim 3, whereinan absolute magnitude of each of the second subpixel voltage and a thirdsubpixel voltage defined as the third voltage relative to the commonvoltage is in a range of about 60-95% of an absolute magnitude of thefirst subpixel voltage.
 6. The liquid crystal display of claim 3,wherein the second and the third subpixel electrodes occupy an areaequal to or smaller than about 80% of an area of the pixel electrode. 7.The liquid crystal display of claim 3, wherein a ratio of an area ofeach of the second and the third subpixel electrodes relative to an areaof the first subpixel electrode is about 1-5.
 8. The liquid crystaldisplay of claim 3, further comprising a coupling electrode connected tothe first subpixel electrode and overlapping the second and the thirdsubpixel electrodes for forming the capacitive coupling.
 9. The liquidcrystal display of claim 8, wherein the coupling electrode has first andsecond portions overlapping the second and the third subpixelelectrodes, respectively, and the first and the second portions of thecoupling electrode have different widths.
 10. The liquid crystal displayof claim 9, wherein overlapping areas between the coupling electrode andthe second and the third subpixel electrodes are different.
 11. Theliquid crystal display of claim 3, further comprising a fourth subpixelelectrode capacitively coupled with the first to the third subpixelelectrodes and having a fourth voltage.
 12. The liquid crystal displayof claim 11, wherein relative value of a sum of the first subpixelvoltage and the third subpixel voltage and a sum of the second subpixelvoltage and a fourth subpixel voltage defined as the fourth voltagerelative to the common voltage is in a range of about 80-100%.
 13. Theliquid crystal display of claim 1 1, further comprising a couplingelectrode connected to the first subpixel electrode and overlapping thesecond to the fourth subpixel electrodes for forming the capacitivecoupling.
 14. The liquid crystal display of claim 13, wherein thecoupling electrode has first to third portions overlapping the second tothe fourth subpixel electrodes, respectively, and the first to the thirdportions of the coupling electrode have different widths.
 15. The liquidcrystal display of claim 14, wherein overlapping areas between thecoupling electrode and the second to the fourth subpixel electrodes aredifferent.
 16. The liquid crystal display of claim 1, wherein the secondsignal line comprises a curved portion including at least tworectilinear portions alternately arranged with making clockwise andcounterclockwise angles with the first signal line.
 17. The liquidcrystal display of claim 1, wherein the pixel electrode has a shape ofcurved stripes that is curved at least twice and the first subpixelelectrode and the second subpixel electrode is divided at curvedportions of the pixel electrode.
 18. The liquid crystal display of claim17, wherein the pixel electrode and the common electrode comprise a tiltdirection determining member curved following the shape of the pixelelectrode.
 19. The liquid crystal display of claim 1, further comprisinga storage electrode line that extends substantially parallel to thefirst signal line and includes a storage electrode overlapping the pixelelectrode.
 20. A liquid crystal display comprising: a first panelincluding a first signal line, a second signal line intersecting thefirst signal line, a thin film transistor connected to the first and thesecond signal lines, and a pixel electrode connected to the thin filmtransistor and including a first subpixel electrode and a plurality ofsecond subpixel electrodes separated from each other and capacitivelycoupled to the first subpixel electrode; a second panel including acommon electrode facing the pixel electrode and supplied with a commonvoltage; and a vertically aligned liquid crystal layer that isinterposed between the pixel electrode and the common electrode, whereinthe first and the second subpixel electrodes have first and secondsubpixel voltages relative to the common voltage and the second subpixelvoltages have different voltage ratios with respect to the firstsubpixel voltage.
 21. The liquid crystal display of claim 20, wherein anabsolute magnitude of each of the second subpixel voltages is lower thanan absolute magnitude of the first subpixel voltage.
 22. The liquidcrystal display of claim 21, wherein the number of the second subpixelelectrodes is two.
 23. The liquid crystal display of claim 22, whereinthe first subpixel electrode has an area equal to or smaller than anarea of the second subpixel electrodes.
 24. The liquid crystal displayof claim 22, wherein the absolute magnitude of each of the secondsubpixel voltages is in a range of about 60-95% of an absolute magnitudeof the first subpixel voltage.
 25. The liquid crystal display of claim22, wherein the second subpixel electrodes occupy an area equal to orsmaller than about 80% of an area of the pixel electrode.
 26. The liquidcrystal display of claim 22, wherein a ratio of an area of each of thesecond subpixel electrodes relative to an area of the first subpixelelectrode is about 1-5.
 27. The liquid crystal display of claim 22,further comprising a coupling electrode connected to the first subpixelelectrode and overlapping the second subpixel electrodes for forming thecapacitive coupling.
 28. The liquid crystal display of claim 27, whereinthe coupling electrode has a plurality of portions overlapping thesecond subpixel electrodes, respectively, and having different widths.29. The liquid crystal display of claim 28, wherein overlapping areasbetween the coupling electrode and the second subpixel electrodes aredifferent.
 30. The liquid crystal display of claim 20, wherein thenumber of the second subpixel electrode is three.
 31. The liquid crystaldisplay of claim 30, further comprising a coupling electrode connectedto the first subpixel electrode and overlapping the second subpixelelectrodes for forming the capacitive coupling.
 32. The liquid crystaldisplay of claim 31, wherein the coupling electrode has a plurality ofportions overlapping the second subpixel electrodes, respectively, andhaving different widths.
 33. The liquid crystal display of claim 32,wherein overlapping areas between the coupling electrode and the secondsubpixel electrodes are different.
 34. A liquid crystal displaycomprising: a first panel including a first signal line, a second signalline intersecting the first signal line, a thin film transistorconnected to the first and the second signal lines, and a pixelelectrode connected to the thin film transistor and including aplurality of subpixel electrodes separated from each other; a secondpanel including a common electrode facing the pixel electrode andsupplied with a common voltage; and a vertically aligned liquid crystallayer that is interposed between the pixel electrode and the commonelectrode, wherein the subpixel electrodes have different voltages andone of the second subpixel electrodes having a higher voltage has anarea equal to or smaller than another of the second subpixel electrodeshaving a lower voltage.